exhaust smell when the furnace kicks on
You must have a vent from the outside to admit combustion air/oxygen for the furnace. This is preferably in the basement so as not to suck heated air from the living space. Do you have a basement window you can leave ajar to see if that cures the odor problem?
There should be an air intake for the combustion chamber of the furnace, generally near floor level. If vapors or smoke come out of that, then you have a venting problem either within the furnace or in the chimney or having to do with circulation and venting of the house itself.
In older construction, the less meticulously sealed cracks such as around windows sufficed as air vents. Seal up cracks in ductwork.
In the event of a cracked heat exchanger letting combustion gases become commingled with room air in a hot air system, you really should shut the whole thing down until appropriate repairs (usually requires replacement) can be done. Get a CO (carbon monoxide) detector and test various areas in the living space above a day at a time.
If the basement is not used as living space (playroom, etc.) there should be no heat vents or return vents in use down there.
Last edited by AllanJ; 01-19-2009 at 09:29 AM.